...with A: being a 3.5" floppy, and B: being an even floppier 5.25"
Just a note for historical accuracy, if we're talking about the early days of IBM PC/MS-DOS machines, A: was reserved for a 5¼" floppy drive whilst B: was reserved for those with the desire and dosh for a second floppy drive - really handy for things like saving data. Of course, Winchester disks (as early HDDs were commonly known) plugged into a PC were just a dream.....not least because, surely, no-one needed more than 360K storage.